1. Field of the Invention
The present invention relates to thin film formation devices. Specifically, the present invention relates to evaporation devices having a mechanism which can form a film using a material by an evaporation method. The material is a material which can be formed as a film by an evaporation method.
2. Description of the Related Art
In recent years, thin and flat display devices have been needed as display devices in televisions, cellular phones, digital cameras, and the like, and as the display devices satisfying this need, display devices using self-light emitting elements have attracted attention. One of the self-light emitting elements is a light emitting element utilizing electroluminescence (EL), and this light emitting element includes a light emitting material interposed between a pair of electrodes and can provide light emission from the light emitting material by voltage application.
Such self-light emitting elements have advantages over liquid crystal display elements, such as high visibility of the pixels and no need of backlight and are considered suitable as flat panel display elements. Another major advantage of such light emitting elements is that they can be manufactured to be thin and lightweight. In addition, extremely high response speed is also one of the features.
Further, such a self-light emitting element can be formed into a film shape; therefore, surface light emission can be easily obtained by formation of a large-area element. Since this feature is hard to obtain from a point light source typified by an incandescent light bulb or an LED, or a linear light source typified by a fluorescent lamp, the self-light emitting element has high utility as an area light source which is applicable to a lighting system or the like.
Light emitting elements utilizing electroluminescence are classified according to the type of a light emitting material, that is, an organic compound or an inorganic compound. In general, the former is referred to as an organic EL element, the latter as an inorganic EL element.
Light-emitting materials which are used for organic EL elements using an organic compound are classified into high molecular compounds (polymer) and low molecular compounds (monomer). Such high molecular compound materials are formed as a film by a wet method such as a spin coating method or an inkjet method, while such low molecular compound materials are formed mainly by an evaporation method.
In general, evaporation devices have a holding portion for holding a substrate and an evaporation source holder for holding an evaporation material. In an evaporation device using a resistance heating method, an evaporation source holder is placed between electrodes, and a current is made to flow in a boat, a crucible, a filament or the like in which an evaporation material is held, with use of the electrodes, to heat the evaporation material, thereby forming a film.
However, such electrodes are positioned near a boat, a crucible, and a filament or the like, in which an evaporation material is held, and thus, there is a problem in that an evaporation material is adhered to the electrodes at the time of evaporation. Therefore, when another material is evaporated, maintenance is needed to prevent contamination, in which the electrodes are cleaned to remove the material adhered to the electrodes.
In addition, a large evaporation device has large electrodes and large weight. In addition, in case of an evaporation device having a plurality of evaporation source holders, since it has a plurality of pairs of electrodes, a large amount of labor is needed for washing the electrodes. Such electrodes are needed to be fixed on a plate on which an evaporation source holder is set; and such electrodes are preferably fixed thereon from beneath such a plate so that the fixed portion is prevented from being contaminated. However, when the electrodes are fixed with a screw from beneath the plate on which an evaporation source holder is set, is also needed to be removed together with the electrodes to remove the electrodes for cleaning. The plate for fixing weighs 20 to 30 kg in some cases, and thus, it is hard work to remove materials attacked to the electrodes. When an evaporation device having a plurality of evaporation sources is used, a plate having a plurality of evaporation source holders weighs more and the work operation is harder.